The present invention relates to the automatic packaging of a substance for infusion, such as tea, chamomile, or similar herbal products, in paper filter bags, designed to be immersed in a liquid to prepare the infusion. In particular, the present invention relates to a filter bag with a special structure and the method for its production.
Recent market research has highlighted renewed interest in filter paper bags with a containment chamber which has two compartments, also known as two-lobed filter bags, made by heat-sealing. The filter bag is obtained by folding the filter paper then sealing the folds obtained in this way, using heat to activate a layer of glue spread on the paper web during one of the production steps.
However, filter bags made of heat-sealable filter paper using the conventional method are heavier than bags of the same size and shape in which the chambers which hold the doses of product are obtained by folding alone.
Since the cost of the paper is proportional to its weight, the greater weight of the bags made of heat-sealable filter paper means that, all other conditions being equal, they are more expensive than those made using folding alone. Since they are products with a low absolute weight, even a weight which is just a few grams higher has a significant percentage effect on the overall cost of the bag. To make bags made of heat-sealed paper economically competitive with bags made using folding alone, it is common practice to give the bags made of heat-sealed paper smaller overall dimensions than those of the corresponding bags made of folded paper.
When the bag made of heat-sealed paper is made with the pick-up tag connecting thread wound around the bag and precisely as long as the outline of the bag, the latter's reduced dimensions mean that the working length of the thread available is shorter.
If the infusion is prepared in certain types of tea-pots or in particularly tall cups or glasses, said thread length may be insufficient to prevent the tag from accidentally slipping over the edge of the infusion container during infusion and falling into the infusion liquid, with obvious consequences in terms of hygiene and/or pick-up tag recovery.
Moreover, bags made of heat-sealed paper using the known method, at the production step also involve the use of a blob of adhesive—normally Mylar®, which, attached to the thread and the bag, allows them to be held together in a compact structure, preventing the tag from dangling freely from the bag.
The material used for the blob of adhesive has its own cost, which disadvantageously increases the overall cost of the filter bag. Other costs are also related to the complex construction of the packaging machines which require a purpose-designed unit for the adhesive for the bag.